The present invention relates to the manufacture of tubing to be used in the oil and gas industry either for purposes of immediate and direct conduction of oil and gas or for purposes of use as drill pipes whereby in either case tubes or pipes possibly with thin walls are used to be welded to connecting sleeves to establish a tubular element with threaded ends for use as conduit element e.g. in a pipeline or as element in a string of drill pipes. The tubing or pipes leave preferably relatively thick e.g. upset end portions for connection to connecting sleeves.
Tubing for the oil and gas industry as well as drill pipes to be interconnected are used generally in oil drilling and exploration in great depth or to conduct the oil or gas out of and away from the site. In the latter case at least some of the tubing is used above ground. These tubes or pipes experience a high mechanical load primarily on account of the internal pressure and longitudinal forces. On the other hand drill pipes experience an additional load on account of the weight of the drill head, the weight of the drill pipe itself and the torque resulting from drilling as well as from any bending. Therefore one will almost exclusively use high grade steel tubing and pipes for these purposes which after tempering are connected to coupling or connecting sleeves. Usually these connecting sleeves are of the flange variety or they are particularly thick walled, short tubes with a suitable threading so that a unit composed of a pipe and/or tube proper with connecting sleeve attached to either end can now be interconnected to form a large string of tubing or drill pipes. In the past these connecting sleeves have usually been first threaded onto the respective pipe ends or tube ends and thereafter welded thereto. More recently it has become customary to directly connect the connecting sleeves to the tube or pipe by means of welding and subsequently the welding seam is deburred and stress relieving annealled.
Tubes and drill pipes made in the aforementioned manner satisfy practical requirements as far as particular physical properties are conerned such as yield strength, yield point elongation etc. But in the presence of moist acid gas the load in that sense must not even come close to the yield strength. Particularly the transition zones between the welding seam and the basic material are highly prone to a stress corrosion cracking if the tubing is made in the conventional manner. The resistance against stress corrosion is tested for example in a saturated hydrogen sulfide test solution in accordance with NACE standards TM-01-77.